"The BOJ is buying ETFs as part of its monetary policy steps. Specific means on how it buys is left to the central bank to decide," Abe told parliament.

Under a policy dubbed yield curve control, the BOJ guides short-term interest rates at -0.1% and 10-year government bond yields around 0%. It also buys government bonds and risky assets such as ETFs to funnel money to markets.

(Reporting by Leika Kihara; Editing by Chang-Ran Kim)